The present invention relates to the utilization of a silver-iron material having further additives for electrical contacts.
The essential requirements for an electrical contact material include a high resistance to arc erosion, resistance to welding and a low contact resistance. Depending on the actual demands placed on such objects in operation and the electrical current used, there can be obtained an evaluation with respect to the profile of the requirements for any given situation. For switch gears for low tension application it is known that silver-tin oxide (Ag/SnO.sub.2) materials are suitable because of switch contacts made therefrom are high resistant to arc erosion and are highly resistant to welding when such contacts are closed to conduct, that is the materials ensure against welding. These are particularly good for electrical currents of 100-3000 A. For lower currents, a composite material of silver and nickel has been found suitable. This material, is compared to a fine silver product, exhibits a higher resistance to arc erosion without, however, experiencing any substantial increase in the contact resistance.
A further and frequently utilized composite material is silver-tungsten (Ag/W) which has a high resistance to arc erosion. However when frequent switching connections are made during exposure to air, there is created a surface layer of silver-tungstenate which leads to an increase in the contact resistance.
From the Japanese patent application No. 79/148-109 it is known to provide electrical contact materials which possess in addition to silver the addition materials of iron, nickel, chromium and/or cobalt. In particular, materials which have the composition Ag10Fe display a high resistance to welding and yet have a good electrical conductivity.
Notwithstanding this development, these previously known materials have long failed to achieve a wide utilization, which drawback can be attributable to the formation of oxide layers and which then lead to high contact temperatures.